Detector for detecting information carried by a signal having a sawtooth-like shape

ABSTRACT

A detector for detecting information carried by a signal having a sawtooth-like shape. The detector includes a first band-pass filter with center frequency around a first frequency value for filtering the signal and generating a first filtered signal, a second band-pass filter with center frequency around a second frequency value for filtering the signal and generating a second filtered signal, a first comparator for comparing the first filtered signal with a reference level and generating a first compared signal, a second comparator for comparing the second filtered signal with the reference level and generating a second compared signal, a clock generator for generating a reference clock having a frequency close to the first frequency value according to the second compared signal, and a detection module for generating a bit signal representing the information according to the first compared signal and the reference clock.

This application is a Continuation of application Ser. No. 10/923,807,Now U.S. Pat. No. 7,313,753, filed on Aug. 24, 2004, which designatedthe United States, and on which priority is claimed under 35 U.S.C.§120, the entire contents of which are hereby incorporated by reference.This application claims the benefit of the filing date of TaiwanApplication Ser. No. 092123684, filed on Aug. 28, 2003.

BACKGROUND

The invention relates to a detector for detecting information carried bysignal having a sawtooth-like shape, and more particularly to a detectorhaving a filter and a comparator to detect the information carried by asignal having a sawtooth-like shape.

Along with advances in optical disc technologies, a new generation ofthe optical disc rewritable format that is defined as the Blu-Ray hasbeen developed. The track groove in the Blu-Ray optical disc has awobble shape, and the basic wobble pattern of the track groove is asine/cosine wave. In the Blu-Ray optical disc, one nominal wobble length(referred to as NWL hereinafter) is equivalent to 69 channel bits, whichis the minimum record unit of the Blu-Ray optical disc.

The basic pattern of the wobble is a cosine wave: cos {2π*f_(wob)*t},where f_(wob) denotes the basic frequency of the wobble. Wobbles in thisbasic shape are called “Monotone Wobbles” (MW). In addition, somewobbles are modulated in order to carry the address information whichare referred to as the ADIP (Addresses in Pre-groove), of some recordunits on the disc, wherein two modulation methods are involved. Thefirst modulation method is the minimum shift keying-cosine variant(referred to as MSK-cos hereinafter), and the second method is theharmonic modulated wave (referred to as HMW hereinafter).

FIG. 1 shows the definition of the MSK mark (referred to as MMhereinafter). As shown in FIG. 1, one MSK mark consists of three NWLswith the following wobble patterns:

a first NWL starts MSK mark with a cosine wobble with a frequency1.5*f_(wob), and is given bycos {2π*(1.5*f_(wob))*t}  (1)

a second NWL continues the MSK mark with a cosine wobble with afrequency f_(wob), and is given by−cos {2π*f_(wob)*t}  (2)

a third NWL terminates the MSK mark with a cosine wobble with afrequency 1.5*f_(wob), and is given by−cos {2π*(1.5*f_(wob))*t}  (3)

FIG. 2 shows the definition of the sawtooth wobble (referred to as STWhereinafter), which is a wobble having a sawtooth-like shape. A STW isformed by combining the basic cosine wave and a sine wave of the doublefrequency and is given by:cos {2π*f_(wob)*t}±a*sin {2π*(2*f_(wob))*t}  (4)

The coefficient a in equation (4) is 0.25.

Such a combination of a cosine signal with the basic frequency f_(wob)and a weighted second harmonic signal forms a sawtooth-like waveform.The “+” or “−” sign creates the left or right inclination of thewaveform, where the “+” sign is used to represent a bit information oflogic one, while the “−” sign is used to represent a bit information oflogic zero.

FIG. 3 shows the typical ADIP structure of the Blu-Ray optical disc. Thedata to be recorded onto the optical disc must be aligned with the ADIPaddresses which are modulated in the wobble. As shown in FIG. 3, 56 NWLscorrespond to two recording frames and each group of 56 NWLs is calledan ADIP unit. Each recording frame includes 1932 channel bits containinga sync filed and a data field. Moreover, two adjacent ADIP units areseparated by a recording frame having a period of about 9.5 wobblecycles.

FIG. 4 shows the format of an ADIP unit. As shown in FIG. 4, thefollowing types of ADIP units are defined:

monotone unit: consisting of 1 MM followed by 53 MW;

reference unit: consisting of 1 MM followed by 15 MW, 37 STW, and 1 MW;

sync_(—)0 unit: consisting of 1 MM followed by 13 MW, 1 MSK mark, 7 MW,1 MM, and 27 MW;

sync_(—)1 unit: consisting of 1 MM followed by 15 MW, 1 MSK mark, 7 MW,1 MM, and 25 MW;

sync_(—)2 unit: consisting of 1 MM followed by 17 MW, 1 MM, 7 MW, 1 MM,and 23 MW;

sync_(—)3 unit: consisting of 1 MM followed by 19 MW, 1 MM, 7 MW, 1 MM,and 21 MW;

data_(—)1 unit: consisting of 1 MM followed by 9 MW, 1 MM, 3 MW, 37 STW,and 1 MW; and

data_(—)0 unit: consisting of 1 MM followed by 11 MW, 1 MM, 1 MW, 37STW,and 1 MW.

The four kind of sync units are used for synchronization purpose, thedata_(—)1 unit is used to represent a bit information of logic one, andthe date_(—)0 unit is used to represent a bit information of logic zero.Hence, the ADIP addresses on the optical disc are positioned accordingto the unit types of the above-mentioned ADIP unit. So, in order tojudge the unit types of the ADIP unit correctly, it is an importantsubject to correctly detecting the information carried by the STW.

SUMMARY

It is therefore an object of the invention to provide a detector fordetecting the bit information carried by the sawtooth wobble.

The invention achieves the above-identified object by providing adetector for detecting the information carried by a signal having asawtooth wobble. The signal contains a first frequency component that issubstantially at a first frequency value and a second frequencycomponent that is substantially at a second frequency value. The secondfrequency value is lower than the first frequency value. The detectorcomprises a first band-pass filter with central frequency around thefirst frequency value for receiving the signal and generating a firstfiltered signal; a second band-pass filter with central frequency aroundthe second frequency value for receiving the signal and generating asecond filtered signal; a first comparator for comparing the firstfiltered signal with a first reference level and generating a firstcompared signal; a second comparator for comparing the second filteredsignal with a second reference level and generating a second comparedsignal; a clock generator for receiving the second compared signal andgenerating a reference clock having a frequency close to the firstfrequency value; and a detection module for generating a bit signalrepresenting the information carried by the signal according to thefirst compared signal and the reference clock.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the definition of the MSK mark.

FIG. 2 shows the definition of the sawtooth wobble.

FIG. 3 shows the architecture of the ADIP information of the Blu-Rayoptical disc.

FIG. 4 shows the format of the ADIP unit.

FIG. 5 shows the block diagram of the detector of the present invention.

FIGS. 6A to 6E are schematic illustrations showing the waveforms of thesignals within the detector of the invention, wherein FIG. 6A shows thewobble signal, FIG. 6B shows the second compared signal, FIG. 6C showsthe reference clock, FIG. 6D shows the first compared signal, and FIG.6E shows the differential signal.

FIGS. 7A to 7E are schematic illustrations showing the waveforms of thesignals within the detector of the invention, wherein FIG. 7A shows thewobble signal, FIG. 7B shows the second compared signal, FIG. 7C showsthe reference clock, FIG. 7D shows the first compared signal, and FIG.7E shows the differential signal.

FIG. 8 shows a flow-chart of a method according to the presentinvention.

DETAILED DESCRIPTION

The detector of the invention for detecting information carried by awobble signal having a sawtooth-like shape will be described withreference to the accompanying drawings.

FIG. 5 illustrates the block diagram of the detector of the presentinvention for detecting information carried by a wobble signal having asawtooth-like shape. Referring to this drawing, the detector 50 includesa first band-pass filter 51, a second band-pass filter 52, a firstcomparator 53, a second comparator 54, a clock generator 55, and adetection module 56.

Let the base frequency of the wobble signal is denoted by f_(wob). Asabove described, the sawtooth wobble mainly contains two frequencycomponents, one is the base frequency component, and the other is thedouble-frequency component. The first band-pass filter 51 has its centerfrequency f_(c1) close to twice the base frequency f_(wob). The firstband-pass filter 51 receives the wobble signal and generates a firstfiltered signal A. The second band-pass filter 52 has its centerfrequency f_(c2) close to the base frequency f_(wob). The secondband-pass filter 52 receives the wobble signal and generates a secondfiltered signal C. Hence, after the wobble signal passes through thefirst band-pass filter 51, the base frequency components are filteredout and only the components, i.e. the double-frequency component, nearthe center frequency f_(c1) are output. Ideally, the signal A is givenbyA=±a*sin {2π*(2*f _(wob))*t}  (5)

Practically, the signal A will be attenuated by the first filter andsuffer from noise or interference.

On the other hand, after the wobble signal passes through the secondband-pass filter 52, the double-frequency component is filtered out andonly the components, i.e. the base frequency component, near the basefrequency f_(c2) are output. Ideally, the signal C is given byC=cos {2π*f _(wob) *t}  (6)

Practically, the signal C will be attenuated by the first filter andsuffer from noise or interference.

The first comparator 53 converts the first filtered signal A into afirst compared signal B having a square waveform, and the secondcomparator 54 converts the second filtered signal C into a secondcompared signal D having a square waveform. For practicalimplementation, the first comparator 53 and the second comparator 54 maybe, as an example, a slicer. That is, when the level of the firstfiltered signal A is higher than the reference voltage, the firstcompared signal B is at logic high; otherwise the first compared signalB is at logic low. Similarly, when the level of the second filteredsignal C is higher than the reference voltage, the second comparedsignal D is at logic high; otherwise the second compared signal D is atlogic low. The clock generator 55 is used to generate a reference clockF having a frequency twice that of the second compared signal Daccording to the second compared signal D. As an example, the clockgenerator 55 could be a typical PLL (Phase-Locked Loop).

The detection module 56 receives the first compared signal B andreference clock F and outputs a bit signal to represent the bitinformation carried by the sawtooth wobble. The detection module 56, forexample, includes an XOR gate 561 and a detection unit 562. The XOR gate561 receives the reference clock F of the clock generator 55 and thefirst compared signal B, and outputs a differential signal G Thedetection unit 562 receives the differential signal G and outputs thebit signal according to the duty cycle of the differential signal G Ifthe duty cycle of the differential signal G is greater than 50%, i.e.the high level portion of the differential signal G is greater than itslow level portion, the detection unit 562 outputs the bit signal withbit value of 1; and when the duty cycle of the differential signal G issmaller than 50%, i.e. the high level portion of the differential signalG is lower than its low level portion, the detection unit 562 outputsthe bit signal with bit value of 0.

For implementation, the detection unit 562 may be implemented using acounter (not shown) and a comparator (not shown). To speak morespecifically, the counter is used to count the pulse number of acounting clock, which has a frequency higher than that of thedifferential signal G, when the differential signal G is at high levelduring each cycle of the differential signal G. The comparator comparesthe obtained pulse number with a threshold value. When the obtainedpulse number is higher than the threshold value, it means that the dutycycle is greater than 50% and the detection unit 562 will output the bitsignal with bit value of 1; and when the obtained pulse number is lowerthan the threshold value, it means that the duty cycle is lower than 50%and the detection unit 562 will output the bit signal with bit value of0. Note that, the detection unit may be implemented in various ways, andthese detection units may be used with the present invention. Suchdetection units include, but are not limited to above discloseddetection unit.

FIGS. 6A to 6E are schematic illustrations showing the waveformssimulated by the detector of the invention, wherein FIG. 6A shows thewobble signal, FIG. 6B shows the second compared signal D, FIG. 6C showsthe reference clock F, FIG. 6D shows the first compared signal B, andFIG. 6E shows the differential signal G As shown in FIG. 6A, the wobblesignal is a rightward slanting sawtooth wobble, so the bit informationcarried by the sawtooth wobble should be 1. After being filtered by thesecond band-pass filter 52 and sliced by the comparator 54, thefrequency of the second compared signal D is substantially the basefrequency f_(wob), as can be seen in FIG. 6B. The reference clock F ofFIG. 6C is generated by the PLL according to the second compared signalD, and the phase thereof is the same as that of the second comparedsignal D. The first compared signal B of FIG. 6D is generated by thecomparator 53. So, as shown in FIG. 6D, the frequency of the firstcompared signal B is substantially 2*f_(wob). The differential signal Gof the FIG. 6E is generated by performing XOR operation on the referenceclock F and first compared signal B.

Hence, as shown in FIG. 6E, the duty cycle of the differential signal Gis greater than 50%. In other words, the high level portion of thedifferential signal G is greater than its low level portion. Since theduty cycle is greater than 50%, the detection unit 562 will correctlyoutput the bit signal with bit value of 1, which is just the expectedone.

FIGS. 7A to 7E are schematic illustrations showing the waveformssimulated by the detector of the invention, wherein FIG. 7A shows thewobble signal, FIG. 7B shows the second compared signal D, FIG. 7C showsthe reference clock F, FIG. 7D shows the first compared signal B, andFIG. 7E shows the differential signal G As shown in FIG. 7A, the wobblesignal is a leftward slanting sawtooth wobble, so the bit informationcarried by the sawtooth wobble should be 0. After being filtered by thesecond band-pass filter 52 and sliced by the comparator 54, thefrequency of the second compared signal D is substantially the basefrequency f_(wob), as can be seen in FIG. 7B. The reference clock F ofFIG. 7C is generated by the PLL according to the second compared signalD, and the phase thereof is the same as that of the second comparedsignal D. The first compared signal B of FIG. 7D is generated by thecomparator 53. So, as shown in FIG. 7D, the frequency of the firstcompared signal B is substantially 2*f_(wob). The differential signal Gof the FIG. 7E is generated by performing XOR operation on the referenceclock F and first compared signal B.

Hence, as shown in FIG. 7E, the duty cycle of the differential signal Gis less than 50%. In other words, the high level portion of thedifferential signal G is less than its low level portion. Since the dutycycle is less than 50%, the detection unit 562 will correctly output thebit signal with bit value of 0, which is just the expected one.

FIG. 8 shows a flowchart of a method for detecting information carriedby a signal having a sawtooth-like shape according to the presentinvention. The signal contains a first frequency component that issubstantially at a first frequency value and a second frequencycomponent that is substantially at a second frequency value. The secondfrequency value is lower than the first frequency value. As an example,the first frequency value is twice the second frequency value.

The method comprises the steps of:

Step S802: receive the signal.

Step S804: filter the signal based on a central frequency around thefirst frequency value and generating a first filtered signal.

Step S806: filter the signal based on a central frequency around thesecond frequency value and generating a second filtered signal.

Step S808: compare the first filtered signal with a first referencelevel and generating a first compared signal.

Step S810: compare the second filtered signal with a second referencelevel and generating a second compared signal. The first reference leveland the second reference level may be the same.

Step S812: generate a reference clock having a frequency close to thefirst frequency value according to the second compared signal.

Step S814: generate a bit signal representing the information carried bythe signal according to the first compared signal and the referenceclock. Firstly, the method generates a differential signal by performingXOR operation on the first compared signal and the reference clock.Then, the method outputs the bit signal with bit value of 1 when theduty cycle of the differential signal is greater than a threshold;otherwise, the method outputs the bit signal with bit value of 0 whenthe duty cycle of the differential signal is smaller than the threshold.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific construction andarrangement shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

1. A detector for detecting information carried by an input signalhaving a sawtooth-like shape, the input signal contains a firstfrequency component that is substantially at a first frequency value anda second frequency component that is substantially at a second frequencyvalue, the second frequency value being lower than the first frequencyvalue, the detector comprising: a first band-pass filter with centralfrequency around the first frequency value for receiving the inputsignal and generating a first filtered signal; a first comparator forcomparing the first filtered signal with a first reference level andgenerating a first compared signal; a second comparator for comparingthe input signal with a second reference level and generating a secondcompared signal; a clock generator for receiving the second comparedsignal and generating a reference clock having a frequency close to thefirst frequency value; and a detection module for generating a bitsignal representing the information carried by the input signalaccording to the first compared signal and the reference clock.
 2. Thedetector according to claim 1, wherein the first frequency value istwice the second frequency value.
 3. The detector according to claim 1,wherein the first reference level and the second reference level are thesame.
 4. The detector according to claim 1, wherein the detector furthercomprises a second band-pass filter with central frequency around thesecond frequency value for receiving the input signal and generating asecond filtered signal.
 5. The detector according to claim 4, whereinthe second comparator is to receive the second filtered signal togenerate the second compared signal.
 6. The detector according to claim5, wherein the threshold is 50%.
 7. The detector according to claim 1,wherein the clock generator is a PLL (Phase-Locked Loop).
 8. Thedetector according to claim 1, wherein the detection module comprises:an XOR gate for receiving the first compared signal and the referenceclock and generating a differential signal; and a detection unit forreceiving the differential signal, outputting the bit signal with bitvalue of 1 when the duty cycle of the differential signal is greaterthan a threshold, and outputting the bit signal with bit value of 0 whenthe duty cycle of the differential signal is smaller than the threshold.9. A method for detecting information carried by an input signal havinga sawtooth-like shape, the input signal contains a first frequencycomponent that is substantially at a first frequency value and a secondfrequency component that is substantially at a second frequency value,the second frequency value being lower than the first frequency value,the method comprising the steps of: receiving the input signal;filtering the input signal based on a first central frequency around thefirst frequency value and generating a first filtered signal; comparingthe first filtered signal with a first reference level and generating afirst compared signal; comparing the input signal with a secondreference level and generating a second compared signal; generating areference clock having a frequency close to the first frequency valueaccording to the second compared signal; and generating a bit signalrepresenting the information carried by the input signal according tothe first compared signal and the reference clock.
 10. The methodaccording to claim 9, wherein the first frequency value is twice thesecond frequency value.
 11. The method according to claim 9, wherein thefirst reference level and the second reference level are the same. 12.The method according to claim 9, wherein the method further comprisesthe step of filtering the signal based on a second central frequencyaround the second frequency value and generating a second filteredsignal.
 13. The method according to claim 12, wherein the step ofcomparing the input signal with a second reference level is to comparingthe second filtered signal with a second reference level to generate thesecond compared signal.
 14. The method according to claim 9, wherein thestep of generating the bit signal comprises the steps of: generating adifferential signal by performing XOR operation on the first comparedsignal and the reference clock; outputting the bit signal with bit valueof 1 when the duty cycle of the differential signal is greater than athreshold; and outputting the bit signal with bit value of 0 when theduty cycle of the differential signal is smaller than the threshold. 15.The method according to claim 14, wherein the threshold is 50%.